JPH0146170B2 - - Google Patents

Description

[Detailed description of the invention]

In a hollow chamber provided for the flow of gas and surrounded by a gas-tight jacket, the invention comprises:
Interaction of atoms or molecules with particulates (interactions between particles and filter materials include adsorption of particles, penetration of particles into the filter material, diffusion of particles within the material, and attachment of particles to the material and generation of gases. Flow refers to a substance that exists as fine particles of atoms or molecules, in which a filter material is provided that acts to retain these fine particles. This invention relates to a filter that purifies gas. In known filters of this type, it is known that the filter material consists of bulk material, for example granular material, which is provided in a filter jacket through which the gas flows. In this case, bulk pieces of material with the largest possible surface area are used. When designing this filter, for example, determining the through-flow length l of the filter material through which the through-flow takes place,
Starting from experimental values known for a given filter material. A disadvantage of the known filters is that the bulk material has a large pressure loss, so that the known filters cannot generally be used in the main pipes of the installation. The object of the invention is to purify a flowing gas of substances present as fine particles of atoms or molecules with a high efficiency despite having the lowest possible coefficient of resistance to the gas flow. The purpose is to provide a filter for The problem underlying the invention is solved by a filter of the above-mentioned type according to the invention as follows. That is, channels for the flow of the gas, in which the filter material is made of a material with the greatest possible retention capacity for the fine particles and are present in a regular arrangement and extend over the through-flow length l of the filter material. , and the length l and its hydrodynamic diameter d _eff are expressed as l/d _eff ·St' (where d _eff = 4V ₀ /F: Hydrodynamic diameter in cm, l: length of the filter material in cm, V ₀ : internal volume of the hollow chamber remaining after placing the filter inside the jacket of length l in cm ³ , F: volume in cm ² St' = h/V: second Stanton number, h: mass transfer rate in cm/sec, V: gas flow rate in cm/sec.) The geometrical shape of the filter is selected and constructed such that the product obtained from . The reason will be explained later. Furthermore, in order to adapt the filter according to the invention to the desired operating conditions as widely as possible, a large number of filters of various dimensions, differing with respect to the substances used for the filter material, are tested in order to obtain an optimum filter variant. It is advantageous to do so. A very preferred embodiment of the above embodiments of the filter according to the invention is such that the filter material is free for gas to flow through and has a large number of channels in a regular arrangement, or the filter material is tubular and It is arranged in a hollow chamber, so that the gas flows longitudinally through this filter material. It is also advantageous for the filter material to be rod-shaped and arranged in the hollow chamber in such a way that the gas flows around the filter material longitudinally and transversely. A highly preferred embodiment of the filter according to the invention consists in the following. That is, said length l and said hydrodynamic diameter
d _eff to the filter for a given gas containing said substance, a given flow rate of this gas, and a given substance retained in the filter material, for the desired operating time of the filter. The permeability coefficient is equal to the quotient of the particle flow rate j (l, t) when leaving this filter divided by the particle amount j (o, t) entering the filter: δ (l, t) = j (l, t) / j ( o, t) is set to correspond to a predetermined value e ^-De , δ(l, t) = e ^-De , and η ^* √<1, and for De the following relationship is established. The formula holds true. (In the formula, De: Huon der Detken number (newly introduced name)

It is shown by [Formula]. α: Deposition probability for fine particles on the surface of the filter material (if no activation method is performed, α is approximately equal to 1 at partial pressure P10 ^-10 atm) A: Mass number of fine particles T: Filter material indicated by 〓 The surface temperature of 〓 ^* 〓{h+(1-β)α ^* /α ^* +h} is shown in sec ^-1

[Formula] (Desorption constant expressed in sec ^-1 ) ω ₀ = ~1.308×10 ¹¹ T Thebeian frequency expressed in sec ^-1 Q: Desorption energy expressed in Cal/Mol R: Universal expressed in Cal/(°) Mol Gas constant λ: Decay constant of radioactive material expressed in sec ^-1 I ₁ (x): Transformed Betzell function ζ=4l/d _eff・St′・hα ^* 〓β/(α ^* +h) ² sec ^-1
Indicated by 1-β: Permeability coefficient; probability of irreversibly binding particulates t: Expected operating time of the filter

[Formula]: Unit step Tup function

It is shown by [Formula]. D: Diffusion coefficient of filter material for fine particles η=(1−β)α ^*・N _G /φ _∞ It is expressed as cm/sec. N _G : Density of gas particles in Atome/ ^cm3 φ _∞ : Expected material can be absorbed in unit volume
It means the maximum number of fine particles expressed in Atome/ ^cm3 . ) The filters according to the embodiments described above are optimally adapted to the set conditions and thus also to the particularities of the device. The abovementioned values are therefore set in such a way that the Von der Detken number is as large as possible or at least achieves the value required to obtain the desired value for the transmission coefficient. On the basis of the above-mentioned mathematical relations, testing of filters for large devices can advantageously be carried out on a small model scale, so as to save costs. If the two filters have the same permeability coefficient δ, i.e. the same Von der Detken number De, then the deposition effect,
That is, they are equivalent in terms of filter action. A simple filter modification therefore also makes it possible to obtain the necessary parameter values for the manufacture of filters for use in large installations, for example starting from a straight piece of pipe material through which the gas to be purified flows. At this time, this simple filter is placed under the influence of various operating conditions, and the above parameter values are obtained by the relational expressions. In the case of the filters of the embodiments described above, the diffusion of these particles into the filter material is also taken into account. Therefore,
Advantageously, filters can be made that can operate at temperatures from 400°C to about 1000°C. In contrast, in the known design of filters, only the desorption and adsorption of the fine particles on the surface of the filter material or the chemical reaction of the fine particles with the surface of the filter material are taken into account, the largest possible Efforts were made to use the surface. This has resulted in many known filters lacking the necessary efficiency in the temperature range above 400°C. This is because the temperature of the filter must be maintained at a low temperature by the cooling effect. In order to increase the activity of these known filters, a larger number of filters are connected one after the other, resulting in bulky purification devices. Another preferred embodiment according to the invention is that for the case where the desired temperature of the filter material is below 400° C., this filter material consists of a material for which the following relation holds true: for this material, the relation a 2 If √≪1 and (λ+〓 ^* )t≪1 or the relation b λ≫〓 ^* holds for radioactive materials, then the von der Detken equation that sets the length l and hydrodynamic diameter d _eff of the filter The desired value can be reached according to the numerically simplified equation De=4l/d _eff · St' · α ^* / α ^* + h . . . In the case of the filter of this embodiment, adsorption-desorption equilibrium has not been reached for the adsorption of fine particles on the surface of this filter material (both the decay and desorption of the substance can be ignored). If condition (b) is satisfied (disintegration is more dominant than desorption of the substance), then condition (a) is satisfied for all values of t, and is created according to the relational expression. The filter can be activated indefinitely in time. According to the relational expression, a material with a sufficient deposition probability for the fine particles to be retained is used, and the dimensions of the filter are determined so that the desired transmission coefficient δ is either as small as possible or equal to a predetermined value. is designed to be. Another preferred variant of the filter according to the invention provides that the filter material has a permeability coefficient as high as possible (1-
β), and the following relational expression holds for this material: 2√≫1 and (λ+〓 ^* ) t>2√ and 〓 ^* ≫λ Set its length l and hydrodynamic diameter d _eff De=4l/d _eff・St′(1−β)・α ^* /h+(1−β
)・α ^* ..., the desired value can be reached. In the above-mentioned variant of the filter according to the invention, an adsorption-desorption equilibrium is reached for the deposition of the fine particles on the surface of the filter material, while the diffusion of these fine particles into the filter material is fully exploited. Even in this case, the dimensions of the filter should be designed so that De is as large as possible or the transmission coefficient δ is a desired value. respectively according to the selection of filter material and filter dimensions.
Even at high temperatures of up to 1000° C., such filters have a high degree of activity. Further highly preferred variants of the filter according to the invention are as follows. That is, a constant low transmission coefficient δ
The thickness ε of this filter material in order to obtain the longest possible operating time t for radioactive substances is For non-radioactive substances, it is designed so that the relational expression ε≫√ holds true. Here, D is the diffusion constant for fine particles in the filter material (cm ² /sec)
It is. In particular, in the case of this filter deformation, unlike the filter deformations previously known when producing filters, not only the adsorption-desorption behavior on the surface of the filter material is applied, but also the diffusion of fine particles into the filter material. Whereas in the case of known filters the service life of the filter depends exponentially on the reciprocal of the temperature, in the filter according to the invention the diffusion of particulates into the filter material is fully exploited, so that it can be used particularly at high temperatures. However, it has a long operating life (time) t. The relational expression l/d _eff · St' must have a maximum value considering the geometric shape of the filter, and if it has a maximum value, the average time for particles to reach the wall of the filter is This is shorter than the time the particles stay inside. This means that the particles are in the gas phase for a short time and are therefore very well able to reach the wall and penetrate through this wall into the filter material. The particles are present within the material and the particles remain. This is because the residence time of the particles within the filter material is long. This means that particles are trapped within the filter material and remain in the gas phase only for a short time. The greater this effect of the filter, the more particles remain within the filter material for as long as possible. Therefore, in order to maximize the effectiveness of the filter, the value of l/d _eff ·St' must be maximized. On the other hand, if the value of the above equation is small, the average time for the particles to reach the wall of the filter material will be long. This means that the particles remain within the gas phase so that they do not reach into the filter material. The trapping of particles within the filter material is as low as the filter effect. As described above, since the filter according to the present invention can be used even at high temperatures, it can be advantageously used to purify the cooling gas of a gas-cooled nuclear reactor. And the cooling device required in the case of a normal filter can be omitted. Another highly advantageous application according to the invention is the arrangement of this filter in the main gas stream of a nuclear reactor to be cooled. In the first embodiment described below, attached drawings Nos. 1 and 2 are used.
With reference to the diagram shown in the figure, possible variants of the design data of a filter according to the invention are explained, starting from a given material for this filter material and taking into account various operating conditions. In the second and third examples, the results of experimental studies of multiple filters are compared with the values obtained according to the relational expression for the transmission coefficient δ. Further, in the fourth to sixth embodiments, design data of filter deformations according to the present invention provided for various operating conditions are shown. First Example In order to obtain design data for a filter consisting of a large number of tubes arranged in parallel to each other, the Von der Detzken number De is calculated from the relational expression, and from De the transmission coefficient δ is calculated for a single tube. is calculated back according to the mass flow of gas m〓 flowing through . One tube used in this calculation has a length l = 800
cm and the diameter d=1 cm. The throughput range considered is from 10 ^-2 to 12 g/sec. The gas temperature and the wall temperature of one tube are 950℃, and the gas pressure P = 40
Being crowbarred. Cesium-137 atoms are considered to be particulates that should be purified from helium.
Two different wall materials with permeability coefficients 1-β=0.7‰ and 1-β=100% are assumed here. For Cs−137, a value of 0.7‰ is characteristic for materials with face-centered cubic lattice, whereas 100‰
A permeability coefficient of % means that the material used is a perfect "diffuser". With respect to the schematic diagram of the characteristic curve of the filter described above, the mass throughput is varied according to the parameter K determined by the following relational expression. m〓=K×m〓′ ₀ where m〓 ₀ is a provisional standard mass throughput. Since a linear relationship holds true between the Reynolds number Re and the mass throughput m〓, the following relational expression also holds true. Re=K×Re ₀ where Re ₀ is the Reynolds number of the assumed mass throughput m〓 ₀ . As can be seen from the graphs in Figures 1 and 2 of the attached drawings, the filter characteristic curve for the parameter K has a jump or discontinuity for a constant value of K = 0.077 (due to the difference between turbulent flow and laminar flow). ). The above values for K correspond approximately to the values for the Reynolds number of Re=2300 for the same curve. The above-mentioned discontinuity is constituted by the fact that the shearwood number and thus the mass transfer rate h or the Staunton number St' have a discontinuity similar to the transition from turbulent to laminar flow. The height of the jump described above depends on its geometry, ie the ratio l/d, and on the materials used. Furthermore, it is possible to read from the graph the flow range in which the transmission coefficient δ reaches its minimum value, the Von der Detken number increases accordingly, and the filter efficiency therefore reaches its maximum value. Generally, as can be seen from this graph, the above minimum or maximum value is in the completely laminar flow region or in the transition region of the Reynolds number between about 2500 and 5000, slightly above 2300. When making a filter,
For example, if the filter is made into a tube bundle, the gas flows through the tubes on the outside and on the inside, making it possible to apply both areas simultaneously. In the examples described above, the absolute values shown in the graphs are valid only for the case in question, but the filter characteristic curves shown therein also apply to other operating conditions and to other operating conditions with this filter material. This makes it possible to qualitatively describe other geometric arrangements. The desired absolute value of the efficiency of this filter is readily achieved by suitably providing a large number of tubes in parallel. 2nd Example In order to test the efficiency of a filter consisting of a simple straight pipe, fission products Cs-137,
A helium gas stream containing Cs-134 and Ag-110m is guided through a single tube of 99.5% titanium into two mutually independent tests, and the fission A complete filter was connected to the back of the piece of tubing to check the amount of product. The content of helium fission products in both tests was different. The above single pipe material has a length of 2730 mm, an outer diameter of 24.5 mm, and a wall thickness of
It was 1.65mm. The temperature of the helium entering this filter was in each case 750°C, and the temperature leaving this filter was 210°C in each case. The temperature of the wall of this tube remained stable during operation and could therefore be measured successfully. The helium flow during operation of this filter is 15N
It was adjusted to achieve a throughput of m ³ /hr. The operating time was 785 hours for the first test, and the operating time for the second test was 785 hours.
In the case of the test, it was 1029 hours. To calculate the transmission coefficient δ of this filter and therefore the efficiency of this filter, the following values were substituted into the relation: For Cs-137: 1-β = 0.2‰; Q = 38 Kcal/Mol for Cs-134 For: 1-β = 0.1‰; Q = 38 Kcal/Mol For Ag-110m: 1-β = 0.04‰; Q = 50 Kcal/Mol and ω ₀ = 1.308×10 ¹¹ T sec ^-1 . Due to the temperature gradient in the tubing, the filter was divided into multiple parts for calculation by the equations. The calculated permeability coefficient δ gives an integrated activity value in μCi for the fission products arriving through this filter during the above-mentioned operating time;
It was also compared with the values measured with the perfect filter. The calculated values and experimental values are compared with each other below. 1st test Calculated value Experimental value Cs−137 1.00 1.20 Cs−134 0.97 0.84 Ag−110m 11.4 11.7 2nd test Calculated value Experimental value Cs−137 0.52 0.59 Cs−134 1.6 1.7 Ag−110m 5.1 5.6 3rd example 2nd A filter made of a single piece of stainless steel X10 CrNiTi189 (formerly known as 4541) tube, having the diameter and wall thickness values indicated in the first example, and having a length of 140 cm, in accordance with the tests described in the example. was tested. The temperature of the gas entering the filter was in each case 625°C and leaving the filter at 210°C, and the operating time of the filter was 818 or 790 hours. To calculate the transmission coefficient δ, the following values were substituted into the relation: 1−β=0.7‰ for Cs−137; Q=45Kcal/Mol 1−β=0.33‰ for Cs−134; Q=45Kcal /Mol Ag-110m 1-β = 0.2‰; Q = 28Kcal/Mol and ω ₀ = 1.308×10 ¹¹ T sec ^-1 The following results were obtained: 1st test Calculated value Experimental value Cs-137 2.1 2.2 Cs−134 1.07 0.96 Ag−110m 6.2 6.5 Second test Calculated value Experimental value Cs−137 1.92 2.1 Cs−133 1.03 1.1 Ag−110m 3.26 3.51 Fourth example Design data for a multi-tube filter were obtained for given operating conditions: As can be seen in Figure 3, this filter consists of a large number of parallel tubes at the same distance from each other. ,
The tube is placed inside a jacket 2 surrounding the hollow chamber of this filter. The outer diameter of the individual tubes of this tube bundle is da, the inner diameter of the tubes of this tube bundle is di,
The length of this tube is l and the inside diameter of the jacket is Di. As can also be seen from FIGS. 3 and 4, the tube of this filter allows the gas to be purified to flow through it on the inside and around it on the outside. The gases to be purified are fission products Cs-137 and Ag.
-110m of helium. The expected operating conditions are as follows: Mass throughput of helium: m = 111.25Kg/sec Temperature of helium when entering the filter: T =
950°C Helium pressure: P = 40 bar Expected operating time: t = 30 years The materials used for the above tubes may have a body-centered cubic structure or, for example, Incoloy 802 and Inconel.
A heat-resistant steel with a face-centered cubic structure such as 625 was used. For the materials mentioned above, 1- for Cs-137.
β=0.7‰ and 1−β=0.2‰ for Ag−110m. T = 950°C and P = 40 bar were applied for the binary diffusion coefficients quoted to calculate the mass transfer rate h. D _Cs −He=0.146cm ² /sec D _Ag −He=0.272cm ² /sec Von der Detken number De for h and St′
The values required to calculate are VDI-Heat Table and Pergamon Publishing Int.J.Heat Mass Trausfer Volume 14.
It is found from pages 1235-1259. In the above case, the design data of this filter was calculated according to the relational expression, assuming that the following conditions 2√≫1 and (λ+〓 ^* ) t>2√ and 〓 ^* ≫λ are satisfied. The volume of this filter should not exceed ^40m3 ,
The pressure drop is not higher than 0.11 bar and the permeability coefficient δ for silver is between 6×10 ^-4 and 8.8×10 ^-3 and the permeability coefficient δ for cesium is 1.2×
The design data shown in the table below was calculated for this filter based on the assumption that it is between 10 ^-5 and 2 x 10 ^-3 . In that case, di and da as well as
The values for Di and l are given in cm, where N is the number of parallel tubes of this filter. In addition to these design data, the pressure drop values within this filter in bars are shown as well as the values for the respective permeability coefficients. Values for △P are from VDI-Heat Table and Pergamon Publishing Int.J.Heat.Mass
Calculated according to Trausfer, Vol. 14, pp. 1235-1259.

[Table] Fifth Example Design data for a filter consisting of a number of tubes arranged parallel to each other was obtained under the same operating conditions as in the fourth example, but for a gas inlet temperature of 300°C. 15MoO ₃ ferrite steel was used as the tube material of the above filter. For the above materials, the permeation coefficient, desorption energy Q and binary diffusion coefficient have the following values: For Cs−137 1−β=1.2‰; D _Cs −He=0.039cm ² /sec Q=65Kcal/Mol and ω ₀ =1.308×10 ¹¹ T sec ⁻¹ Ag−110m 1−β= 0.3‰ D _Ag −He=0.072cm ² /sec Q=52Kcal/Mol and ω ₀ =1.308×10 ¹¹ T sec ^-1 In the above case, the following relational expression 2√≪1 and (λ+〓 ^* )t≪1 Design data for this filter was calculated according to the relational expression. The volume of this filter does not exceed 17.2 ^m3 , the pressure drop ΔP is not higher than 0.1 bar, and the permeability coefficient δ for cesium is 1.06×10 ^-4 and the permeability coefficient δ for silver is 5.61×10 ^-6 . The following design data were obtained based on the assumption that N = 10 ⁵ lines Di = 230 cm di = 0.3 cm l = 350 cm da = 0.55 cm Pressure drop ΔP = 0.105 bar. Sixth Example For the operating conditions shown for the fifth example, design data were obtained for a filter consisting of a number of bars placed in a jacket, parallel to each other and at the same distance, similar to the tube described above. . At that time, the fifth
The same materials as shown for the examples but with the following values; transmission coefficient δ = 1.62 x 10 ^-3 for Cs-137 and transmission coefficient for Ag-110m. For δ = 4.4 x 10 ^-5 and assuming that the volume of this filter is 10.5 m ³ and the pressure loss is △P 0.125 bar, we obtained the following results: N = 1.2 x 10 ⁵ pieces l = 250 cm da = 0.5 cm Di = 230 cm The pressure drop was ΔP = 0.124 bar. When the material is the same as in the fifth embodiment and the values for N, da, and Di are the same, the transmission coefficient δ for Cs-137 is 5.84×10 ^-3 and the transmission coefficient δ is for Ag-110m. 3272×10 ⁻⁴ , the length l=200 cm and ΔP=0.11 bar.

[Brief explanation of drawings]

FIG. 1 graphs the Huon der Detken number De as a function of mass throughput or Reynolds number; FIG. 2 graphs the permeability coefficient δ as a function of mass throughput or Reynolds number; FIG. 3 shows a cross section through a filter consisting of a bundle of tubes arranged in parallel, and FIG. 4 shows a longitudinal section through the filter according to FIG. 1...tube, 2...jacket, da...outer diameter of the tube, di...inner diameter of the tube, l...length of the tube, Di...inner diameter of the jacket.

Claims (1)

[Scope of Claims] 1. In a hollow chamber provided for the gas to flow through and surrounded by a gas-tight jacket, a filter material is provided which acts to retain atomic or molecular particles by interaction with these particles. A filter for purifying a flowing gas for substances present as fine particles of atoms or molecules, of the type described, wherein said filter material consists of a material having the greatest possible retention capacity for said fine particles and is present in a regular arrangement. , having a passageway for the flow of said gas extending over a constant length l of the filter material, said length l and its hydrodynamic diameter d _eff such that the pressure drop ΔP and the filter volume are constant. In the case of l/d _eff · St′ (where d _eff = 4V ₀ /F: hydrodynamic diameter in cm, l: length of filter material in cm, V ₀ : length in cm ³ volume of the hollow chamber remaining after placing the filter material inside the jacket in the range l, F: surface area of the filter material wetted by the gas in cm ² , St' = h/V: second Stanton number, h: cm A filter characterized in that it is configured such that the product obtained from the mass transfer rate expressed in cm/sec and V: gas flow velocity expressed in cm/sec becomes a maximum value. 2. A filter according to claim 1, characterized in that the filter material has conduits present in a regular arrangement through which gas freely flows. 3. Claim 3, characterized in that the filter material is tubular and arranged in a hollow chamber, so that the gas flows through it in the longitudinal direction and around it in the longitudinal or transverse direction. The filter according to item 1. 4. A filter according to claim 1, characterized in that the filter material is rod-shaped and arranged in a hollow chamber so that the gas flows around it in a longitudinal or transverse direction. . 5. The filter according to any one of claims 1 to 4, wherein the filter is for purifying cooling gas of a gas-cooled nuclear reactor. 6. The filter according to any one of claims 1 to 4, characterized in that the filter is for installation in the main gas flow of a gas-cooled nuclear reactor.